XD (ConceptTopic, 4)
From Compile Worlds
This is just an expression especially if you think something is too funny for it's own good.
The most awesome use of XD is mentioned above.
A certain Kumizonian is hopelessly addicted of using this over and over again. It's even one of the words they say in their brain!
This little face is often paired with LOL, creating a more obvious link to funniness.